My understanding is that the vaccine is about 80% effective in preventing the disease and lessens disease for the other 20%. I'm always careful to explain this to parents. " Post exposure administration of varivax is not an FDA approved indication for varicella vaccine, its use for this purpose may be effective and confers little risk." Early research said give within 3 days of exposure. Redbook, 1997. Clinically, my associate is big on doing this. I'm not convinced. Haven't seen milder cases at all in sibs who are post-exposure vaccinated. I think it is a waste of $75 :-) You never know if the sib was exposed at the same time as the first case. Wish there was a way to do a carefully controlled study of this. We are very aggressive about giving the vaccine at 12 mo. I have seen much milder cases in children who subsequently get varicella, which isn't frequent. I agree that if mom is unimmunized, it would be a good idea to get vaccine simultaneously with baby, when baby is one yo. When doing a younger sib at one yo, I try to catch any older sibs who don't have a documented case of varicella. Don't forget Dads! I had one case where he was the culprit who brought varicella home :-) Sincerely, Pat in SNJ *********************************************** The LACTNET mailing list is powered by L-Soft's renowned LISTSERV(R) list management software together with L-Soft's LSMTP(TM) mailer for lightning fast mail delivery. For more information, go to: http://www.lsoft.com/LISTSERV-powered.html